I have a bunch of figure 8's, not really sure where they came from. They are all rated at like 40+ KN. I have introduced some people to the sport and I want to build toprope anchors for them and I was wondering if it would be safe to use a figure 8 to run the rope through at the top of a pitch IE: are they safe for multidirectional loads. Also, I could see them coming in handy to build floating anchors for caving, rescue, climbing photography etc. I tried to search for info but was overwhelmed by references to figure 8 knots.

Got some insight into this by looking at some rescue sites. Apparently, before rigging plates where common, figure 8's where standard for collection points. Note that figure 8's made for rescue are usually much stronger than ones made for climbing. The consensus now is that while they may be strong enough to use as collection points it is poor practice to do so because liability for failure shifts to the user when not used in accordance with labeling. A caveat to this is that if you need a lightweight/compact kit for long hikes in or constricted spaces or when you don't have a rigging plate it may be acceptable to substitute a figure 8. Considering how conservative the rescue community is, I am personally comfortable using a fig 8 to set up a toperope where it will never see more than a force factor .5 fall.

Sure, they'll probably work. But the bigger question is, why don't you just use locking carabiners? Why needlessly complicate your toperope system by using equipment and techniques (plates and 8's) designed for rigging and rescue, not climbing? KISS principles generally lead to the safest setups.

A climber competent with basic anchor systems would not even be asking this. Go take a class or read a book on constructing climbing anchors.